The general problem is to furnish a device capable of transmitting in a secure manner a set of high-quality visual films in a format of the MPEG type directly to a TV screen and/or for being recorded on the hard disk of a box connecting the telecommunication network to the television screen while preserving the audiovisual quality yet avoiding any fraudulent use such as the possibility of making pirated copies of films or audiovisual programs recorded on the hard disk of the decoder box.
It is possible with current solutions to transmit films and audiovisual programs in digital form via broadcasting networks of the microwave, cable, satellite, etc. type or via telecommunication networks of the DSL (Digital Subscriber Line) type or BLR (local radio loop) type or via DAB (Digital Audio Broadcasting) networks. Furthermore, in order to avoid the pirating of works broadcasted in this manner, they are frequently encrypted by various means well-known to an expert in the art.
However, the main disadvantage of current solutions (WO 01/65762) is the fact that it is necessary to transmit not only the encrypted data to the users but also the decryption keys. Transmission of the decryption keys can be made before, at the same time as or after the transmission of the audiovisual programs. To increase the security and therefore the protection of audiovisual works against ill-intended usage, the decryption keys as well as the decryption functions of audiovisual decoders can comprise improved security means such as smartcards or other physical keys that can optionally be remotely updated.
Thus, the current solutions applied to a decoder box with the possibility of local recording of audiovisual programs in digital form on any support of the hard disk type or other memory type offer an ill-intentioned user the possibility of making non-authorized copies of programs recorded in this manner since at a given moment this user possesses, with a digital decoder box, whether associated or not with smartcard systems, all the information, software programs and date that permit complete decryption of audiovisual programs. Precisely on account of the fact that the user possesses all the data, the ill-intentioned user has the possibility of making illegal copies without anyone perceiving this fraudulent copy at the moment at which it is made.
One solution would therefore consist of transmitting all or part of a digital audiovisual program solely on demand (on-demand video services) via a broadband telecommunication network of the fiber optic type, ADSL, cable or satellite type without authorizing local recording of audiovisual programs. In this instance, the disadvantage is quite different and stems from the performance of these networks, that do not permit continuous streams of several megabits per second to each user to be guaranteed as required by MPEG streams, that require bandwidths of several hundreds of kilobits at several megabits per second.
Under these conditions, one solution consists of separating the stream into two parts, neither one of which would be usable by itself. For example, EP 0778513 teaches a process that permits the prevention of the illegal use of information by adding control information to it to verify the rights of the user. The system permits permanent knowledge of which part of the information is used and by which user and to know from this information whether the user is illegal or not. Thus, this process secures the data by adding additional information to it that denatures the initial information.
U.S. Pat. No. 5,937,164 makes use of the solution consisting of separating the stream into two parts of which the smallest one holds information necessary for using the largest one. However, that patent is insufficient to responding to the problem identified. In fact, suppressing a part of the stream denatures the format of the stream and it can therefore not be recognized as a standard stream that can be exploited with general software applications. That process requires at the same time specific software on the server side for separating the two parts, and other specific software that ensures not only reconstruction of the stream, but also acquisition of the main stream and its exploitation according to a format proprietary to the solution. That proprietary format is not the initial format of the stream prior to being separated into two parts.
U.S. Pat. No. 5,892,825 resumes the preceding patent, but with a smaller scope because the streams in it are always encrypted U.S. Pat. No. 6,035,329 is based on the same principle and concerns a process permitting reading a disk of the CD-ROM or DVD-ROM type conditioned on the identification of rights by the insertion of a smartcard on which the information necessary for the reading are stored. That process is still not sufficient because it does not guarantee that the modified stream is of the same format as the original stream. Finally, U.S. Pat. No. 6,185,306 relates to a process for the transmission of encrypted data from a Website to a requesting computer. However, that process allows the user to have available at a given moment all the tools necessary for copying the data.